For example, a DC motor with a brush, in which motor magnets are disposed on the inner peripheral surface of a bottomed cylindrical yoke and an armature is rotatably provided on the inside of the motor magnets in a radial direction, is known as an electric motor (for example, see PTL 1).
The armature includes an armature core, armature coils, and a commutator. The armature core includes a plurality of teeth that are provided on the outer periphery of an annular core body externally fitted and fixed to a rotating shaft and radially extend outward in the radial direction. The armature coil is wound on each tooth of the armature core via a slot between the teeth. The commutator is provided on the rotating shaft so as to rotate integrally with the armature core.
The commutator includes a plurality of segments that are disposed side by side in a circumferential direction in a state in which the segments are insulated from each other. Terminal portions of the respective armature coils are connected to these segments.
Further, a plurality of brushes come into sliding contact with the segments. When DC current is supplied to each armature coil through the segment by the brushes, the armature and the rotating shaft are rotated by a magnetic attractive force or a repelling force that is generated between a magnetic field formed on the armature core and the motor magnets. Since the segments with which the brushes come into sliding contact are sequentially changed by the rotation of the armature and the rotating shaft, the switching of the direction of current flowing in the armature coil, that is, so-called rectification is performed. Then, the armature is continuously rotated and a rotational output is taken out of the rotating shaft.
Incidentally, when the commutator rotates, the brushes repeatedly come into contact with the segments and are repeatedly separated from the segments. For this reason, since electric discharge is generated at the time of the separation of the brushes from the segments when a voltage between the segments is high, the lifespan of the brushes are shortened. As means for preventing this, there is, for example, a method of making the number of the segments of the commutator larger than the number of the teeth of the armature core.